The present invention relates to a halogenated polysilane as a pure compound or mixture of compounds each having at least one direct Si—Si bond, whose substituents consist exclusively of halogen or of halogen and hydrogen and in whose composition the atomic ratio substituent:silicon is greater than 1:1.
Such chlorinated polysilanes (PCS) are known, for example, from: DE 10 2005 024 041 A1; DE 10 2006 034 061 A1; WO 2008/031427 A2; WO 81/03168; US 2005/0142046 A1; M. Schmeisser, P. Voss “Über das Siliciumdichlorid [SiCl2]x” [Concerning silicon dichloride [SiCl2]x], Z. anorg. allg. Chem. (1964) 334, 50-56; US2007/0078252A1; DE 31 26 240 C2; GB 702,349; R. Schwarz and H. Meckbach “Über ein Siliciumchlorid der Formel Si10Cl22” [Concerning a silicon chloride of the formula Si10Cl22], Z. anorg. allg. Chem. (1937) 232, 241-248. They can be prepared, on the one hand, by means of a purely thermal reaction, such as described, for example, in M. Schmeisser, P. Voss “Über das Siliciumdichlorid [SiCl2]x”, Z. anorg. allg. Chem. (1964) 334, 50-56 (Schmeisser 1964), by heating vaporous halosilanes with a reducing agent (Si, H2) to relatively high temperatures (>700° C.). The halogenated polysilanes obtained are slightly greenish yellow-colored, glassy and highly polymeric. Furthermore, the literature mixture is strongly contaminated with AlCl3 due to the preparation.
In R. Schwarz and H. Meckbach “Über ein Siliciumchlorid der Formel Si10Cl22”, Z. anorg. allg. Chem. (1937) 232, 241-248, a silicon chloride having the composition Si10Cl22 is further presented, which was obtained by reaction of SiCl4 with silicon carbide at 1050° C. The authors describe it as a highly viscous oil with a molar mass of 1060 g/mol.
Similar results are described by P. W. Schenk and Helmuth Eloching “Darstellung und Eigenschaften des Siliciumdichlorids (SiCl2)x [Preparation and properties of silicon dichloride (SiCl2)x]”, Z. anorg. allg. Chem. (1964) 334, 57-65, who obtain products with molar masses of 1250 (Si12Cl24) to 1580 (Si16Cl32) g/mol as colorless to yellow, viscous to resin-like, cyclic substances.
In R. Schwarz and U. Gregor “Über ein Siliciumchlorid der Formel SiCl” [Concerning a silicon chloride of the formula SiCl], Z. anorg. allg. Chem. (1939) 241, 395-415 a PCS of the composition SiCl is reported. This is completely insoluble.
In J. R. Koe, D. R. Powell, J. J. Buffy, S. Hayase, R. West, Angew. Chem. 1998, 110, 1514-1515, a PCS (cream-white solid) is described, which is formed by ring-opening polymerization of Si4Cl8 and is insoluble in all customary solvents.
In Harald Schafer and Julius Nickl “Über das Reaktions-gleichgewicht Si+SiCl4=2SiCl2 und die thermo-chemischen Eigenschaften des gasformigen Silicium(II)-chlorids” [Concerning the reaction equilibrium Si+SiCl4=2SiCl2 and the thermochemical properties of gaseous silicon (II) chloride], Z. anorg. allg. Chem. (1953) 274, 250-264 and in R. Teichmann and E. Wolf “Experimentelle Untersuchung des Reaktions-gleichgewichtes SiCl4(g)+Si(f)=2SiCl2(g) nach der Strömungsmethode”, [Experimental investigation of the reaction equilibrium SiCl4(g)+Si(f)=2SiCl2(g) according to the flow method], Z. anorg. allg. Chem. (1966) 347, 145-155, thermodynamic investigations on the reaction of SiCl4 with Si are carried out. PCS is not isolated or described here.
In GB 702,349, the reaction of chlorine gas with calcium silicide in a fluidized bed at most 250° C. to give lower perchlorooligosilanes is described. The mixtures formed here are unbranched on account of the low temperature, contain no cyclic PCS and consist of about 80% Si2Cl6 and Si3Cl8 in addition to 11% Si4Cl10 and small amounts of Si5Cl12 and Si6Cl14. The mixtures of these compounds are colorless liquids, contain no cycles and are contaminated by CaCl2 due to the process.
DE 31 26 240 C2 describes the wet-chemical preparation of PCS from Si2Cl6 by reaction with a catalyst. The mixtures obtained still contain the catalyst and are therefore washed with organic solvents, whereby traces of the reactants, the solvents and the catalyst remain. Moreover, these PCSs contain no cyclic compounds.
Further wet-chemical processes are presented in US2007/0078252A1:                1. Halogenated aryloligosilanes to be reduced with sodium and subsequently to be cleaved with HCl/AlCl3 aromatics.        2. Transition metal-catalyzed dehydrogenating polymerization of arylated H-silanes and subsequent dearylation with HCl/AlCl3.        3. Anionically catalyzed ring-opening polymerization (ROP) of (SiCl2)5 with TBAF (Bu4NF).        4. ROP of (SiAr2)5 with TBAF or Ph3SiK and subsequent dearylation with HCl/AlCl3.        
In all these methods, PCSs contaminated with solvent/catalyst are in turn obtained, of which only the distillable fractions can be effectively purified. No product mixture of high purity can therefore be obtained from the above reactions.
It is further known to prepare such halogenated polysilanes via a plasma-chemical process. For example, DE 10 2005 024 041 A1 relates to a process for the preparation of silicon from halosilanes, in which the halosilane is reacted in a first step with generation of a plasma discharge to give a halogenated polysilane, which is subsequently decomposed in a second step with heating to give silicon. This known process is carried out at high energy densities (>10 Wcm−3) with respect to plasma generation, the end product being a not very compact waxy-white to yellow-brownish or brown solid. Spectroscopic investigations have shown that the final product obtained has a relatively large degree of cross-linking. The high energy densities used lead to products of high molar masses, wherefrom insolubility and low fusibility result. Moreover, this PCS also has a significant hydrogen content.
Furthermore, a high-pressure plasma process for the synthesis of HSiCl3 is described in WO 81/03168, in which PCSs are obtained as minor by-products. Since these PCSs are obtained under hydrogenating conditions (HSiCl3 synthesis!), they have a significant hydrogen content.
In US 2005/0142046 A1, a PCS preparation by silent electric discharge in SiCl4 at normal pressure is described. In this process, only short-chain oligosilanes result, as the author shows by example of the selective reaction of SiH4 to give Si2H6 and Si3H8 by connecting several reactors one after the other.
The behavior is analogous in DE 10 2006 034 061 A1, where a similar reaction is described in which gaseous and liquid PCSs are obtained with Si2Cl6 as the main constituent (p. 3, [0016]). Although the authors describe that the molar masses of the PCSs can be increased by use of several reactors connected one after the other, only material can be obtained here that can be brought into the gas phase undecomposed. The authors also express this situation in the claims, in which they provide for distillations for all PCS mixtures obtained. Furthermore, the PCSs mentioned in DE 10 2006 034 061 A1 are hydrogen-containing.
Besides chlorinated polysilanes, further halogenated polysilanes SixHy (X═F, Br, I) are also known in the prior art.
According to F. Höfler, R. Jannach, Monatshefte für Chemie 107 (1976) 731-735, Si3F8 can be prepared from Si3(OMe)8 with BF3 in a closed tube at −50 to −60° C. (8 h) in yields of 55-60%. The methoxyisotetrasilane is completely degraded to shorter perfluorosilanes under these conditions.
E. Hengge, G. Olbrich, Monatshefte für Chemie 101 (1970) 1068-1073 describes the preparation of a 2-dimensionally built polymer (SiF)x. The 2-dimensionally constructed polymers (SiCl)x and (SiBr)x are obtained from CaSi2 by reaction with ICl or IBr. A halogen exchange is then completed with SbF3. However, partial degradation of the Si layer structure occurs here. The resulting product contains the amount of CaCl2 specified stoichiometrically from CaSi, which cannot be washed out.
The preparation of polyfluorosilane (SiF2)x is described, for example, in M. Schmeisser, Angewandte Chemie 66 (1954) 713-714. SiBr2F2 reacts with magnesium in ether at room temperature to give a yellow, highly polymeric (SiF2)x. Compounds such as Si10Cl22, (SiBr)x and Si10Br16 can be transhalogenated with ZnF2 to give the corresponding fluorides.
R. L. Jenkins, A. J. Vanderwielen, S. P. Ruis, S. R. Gird, M. A. Ring, Inorganic Chemistry 12 (1973) 2968-2972 report that Si2F6 decomposes at 405° C. to give SiF4 and SiF2. By condensation of this intermediate, (SiF2)x can be obtained.
The standard method for the production of (SiF2)x is illustrated, for example, in P. L. Timms, R. A. Kent, T. C. Ehlert, J. L. Margrave, Journal of the American Chemical Society 87 (1965) 2824-2828. Here, (SiF2)x is produced by passing SiF4 over silicon at 1150° C. and 0.1-0.2 torr and freezing out the resulting SiF2 at −196° C. with polymerization during the subsequent thawing. The colorless to slightly yellow plastic polymer melts on warming to 200-350° C. in vacuo and releases perfluorinated silanes from SiF4 to at least Si14F30. A silicon-rich polymer (SiF)x remains, which decomposes vigorously at 400±10° C. to give SiF4 and Si. The lower perfluoropolysilanes are colorless liquids or crystalline solids that are isolable by fractional condensation in purities of >95%. Traces of secondary or tertiary amines catalyze the polymerization of the perfluorooligosilanes. U.S. Pat. No. 2,840,588 discloses that SiF2 is formed at <50 torr and >1100° C. from SiF4 and Si, SiC, silicon alloys or metal silicides. For the isolation of (SiF2)x, the intermediate must be cooled rapidly to <0° C. G. P. Adams, K. G. Sharp, P. W. Wilson, J. L. Margrave, Journal of Chemical Thermodynamics 2 (1970) 439-443 describe that (SiF2)x is prepared from SiF4 and Si at 1250° C. In a similar manner, according to U.S. Pat. No. 4,070,444 A (SiF2)x is prepared by reaction of a perfluorosilane with metallurgical silicon and subsequent deposition of the SiF2. Thermolysis of the polymer releases elemental silicon of higher purity than the starting material. The process disclosed in U.S. Pat. No. 4,138,509 A likewise serves for purification. Silicon that contains aluminum as an impurity is reacted with SiF4 in the presence of SiO2 at temperatures >1100° C. in order to produce SiF2. A condensation of the product gas in two stages leads to the selective deposition of the gaseous impurities in a first fraction, while the second fraction consists of largely pure (SiF2)x. Thermal decomposition of the polymer at 100-300° C. produces gaseous and liquid perfluorinated silanes, which are then decomposed to give silicon at 400-950° C.
FI 82232 B discloses a reaction at even higher temperature. SiF4 reacts with Si in an Ar plasma flame to give SiF2 (0.8:1 mol, 70% SiF2 content).
Short-chain perbrominated polysilanes are formed according to A. Besson, L. Fournier, Comptes rendus 151 (1911) 1055-1057. An electrical discharge in gaseous HSiBr3 produces SiBr4, Si2Br6, Si3Br8 and Si4Br10.
K. Hassler, E. Hengge, D. Kovar, Journal of molecular structure 66 (1980) 25-30 prepare cyclo-Si4Br8 by reaction of (SiPh2)4 with HBr under AlBr3 catalysis. In H. Stüger, P. Lassacher, E. Hengge, Zeitschrift für allgemeine and anorganische Chemie 621 (1995) 1517-1522, Si5Br9H is reacted by boiling with Hg(tBu2) in heptane to give the corresponding bis-cyclopenta-silane Si10Br18. Alternatively, a ring linkage of Si5Ph9Br with naphthyllithium or K or Na/K in various solvents can take place with subsequent halogenation with HBr/AlBr3.
Perbrominated polysilanes are described, for example, in M. Schmeisser, M. Schwarzmann, Zeitschrift für Naturforschung 11b (1956) 278-282. In the reaction of Mg turnings with SiBr4 in boiling ether two phases are formed, the lower of which consists of magnesium bromide etherate and (SiBr)x, while the upper phase contains MgBr2 dissolved in ether and small amounts of lower silicon sub-bromides. (SiBr)x can be purified by washing with ether. The reaction of SiBr4 vapor with Si at 1200° C. and in vacuo produces brown, brittle (SiBr2)x. The hydrolysis-sensitive substance is readily soluble in benzene and most non-polar solvents. In vacuo, the polymer decomposes from 200° C. with elimination of Si2Br6. At 350° C. (SiBr)x remains; further warming to 550-600° C. leads to elemental silicon. It is presumed on the basis of the good solubility that (SiBr2)x consists of Si rings of restricted size. The molecular weight determination of about 3000 appears unreliable. (SiBr2)x reacts with Mg in ether to give (SiBr1.46)x. DE 955414 B likewise discloses a reaction at high temperature. If SiBr4 or Br2 vapor is passed through silicon grit in vacuo at 1000-1200° C., mainly (SiBr2)x results in addition to some Si2Br6.
According to M. Schmeisser, Angewandte Chemie 66 (1954) 713-714, in addition to (SiBr)x also Si2Br6 and further oligosilanes such as Si10Br16 are formed by action of SiBr4 on elemental Si at 1150° C.
In US 2007/0078252 A1, the ring-opening polymerization of cyclo-Si5Br10 and cyclo-Si5I10 by action of Bu4NF in THF or DME is claimed.
For example, E. Hengge, D. Kovar, Angewandte Chemie 93 (1981) 698-701 or K. Hassler, U. Katzenbeisser, Journal of organometallic chemistry 480 (1994) 173-175 report on the production of short-chain periodinated polysilanes. By reaction of the phenylcyclosilanes (SiPh2)n (n=4−6) or of Si3Ph8 with HI under AlI3 catalysis, the periodinated cyclosilanes (SiI2)n (n=4−6) or Si3I8 result.
M. Schmeisser, K. Friederich, Angewandte Chemie 76 (1964) 782 describe various routes for the preparation of periodinated polysilanes. (SiI2)x results in about 1% yield on passing SiI4 vapor over elemental silicon at 800-900° C. in a high vacuum. The pyrolysis of SiI4 under the same conditions yields the same very hydrolysis-sensitive and benzene-soluble product. On the action of a glow discharge on SiI4 vapors in a high vacuum, a solid, amorphous, yellow-reddish silicon sub-iodide of the composition (SiI2.2)x insoluble in all customary solvents is obtained with a yield of 60 to 70% (based on SiI4). The pyrolysis of this substance at 220 to 230° C. in a high vacuum leads to a dark-red (SiI2)x, simultaneously forming SiI4 and Si2I6. The chemical properties of the compounds (SiI2)x thus obtained coincide—except for the solubility in benzene. The pyrolysis of (SiI2)x at 350° C. in a high vacuum affords SiI4, Si2I6 and an orange-red, brittle solid of the composition (SiI)x (SiI2)x reacts with chlorine or bromine between −30° C. and +25° C. to give benzene-soluble mixed silicon sub-halides such as (SiClI)x and (SiBrI)x. At higher temperatures, the Si—Si chains are cleaved by chlorine or bromine with simultaneous complete substitution of the iodine. Compounds of the type SinX2n+2 (n=2-6 for X=Cl, n=2-5 for X=Br) are obtained. (SiI2)x reacts completely with iodine at 90 to 120° C. in a bomb tube to give SiI4 and Si2I6.